A high-efficiency furnace typically employs several heat exchangers to warm an air stream passing through the furnace. A high-efficiency furnace is one where approximately 90% of the energy put into the furnace is converted into heat for the purposes of heating the targeted space. These high-efficiency furnaces include “clamshell” or individual panel halves formed by stamping mirror images of the combustion chambers into corresponding metal sheets and coupling them together. Often high-efficiency furnaces comprise a primary heating chamber that includes the clamshell heat exchangers and a secondary heat exchanger/condenser. The air passes through the secondary heat exchanger/condenser from a blower or fan and then passes through the primary heat exchanger. High-efficiency furnaces are also characterized by high operating temperatures. However, cracking problems in the clamshell heat exchanger panels can occur when the temperatures within the heat exchanger consistently exceed about 950 degrees. When such cracks appear, their occurrence is considered a failure of the system.